Solving linear equations in Laplacians and SDD matrices

I am trying to solve linear equations for SDD matrix as follows

a= ring_graph(5)
b = randn(size(la,1))
sddm = copy(la); # doing it with a SDDM matrix
sddm[1,1] += 1;
sol = approxchol_sddm(sddm,verbose=true)
x = sol(b)

In this way the code is working without any problems but if I change the graph to be graph I read it as follows:

a=loadgraph("ieeebus.graphml", "G" , GraphIO.GraphML.GraphMLFormat())
it gives an error messeage
LoadError: MethodError: no method matching extendMatrix(::SparseMatrixCSC{Int64, Int64}, ::Vector{Float64})